Nearly 100 religious groups are urging Congress to keep the 'Johnson Amendment' which limits churches' political activities.
President Donald Trump has vowed to repeal the law which blocks ministers from endorsing political candidates from the pulpit or religious organisations from donating to either party. Many Republicans back him and argue the amendment infringes on religious groups' free speech.
But 99 different groups have written to oppose the move.
'The charitable sector, particularly houses of worship, should not become another cog in a political machine or another loophole in campaign finance laws,' they write.
The strongly worded backlash comes from across the religious spectrum from The Episcopal Church and Baptist groups to Catholic, Jewish, Islamic and Hindu movements.
'Current law serves as a valuable safeguard for the integrity of our charitable sector and campaign finance system,' say in a letter to top members of Congress including Speaker Paul Ryan, House Democratic Leader Nancy Pelosi and chair of Ways and Means Committee Kevin Brady who previously repeal of the amendment would be included in tax-reform legislation.
'People of faith do not want partisan political fights infiltrating their houses of worship,' the signatories, including the National Council of Churches and Islamic Society of North America, write.
'Current law simply limits groups from being both a tax-exempt ministry and a partisan political entity.'
They say repealing the amendment, named after former US President Lyndon Johnson who introduced it as a Senator, would be 'highly divisive' and have a 'detrimental impact' on community life.
'Houses of worship are spaces for members of religious communities to come together, not be divided along political lines; faith ought to be a source of connection and community, not division and discord.'
They also warned the integrity of churches and other places of worship would be tarnished if they were tied to political campaigns.
'If houses of worship endorse candidates, their prophetic voice, their ability to speak truth to power as political outsiders, is threatened.
'The credibility and integrity of congregations would suffer with bad decisions of candidates they endorsed. Tying America's houses of worship to partisan activity demeans the institutions from which so many believers expect unimpeachable decency.'